Java .parallelStream() with spring annotated methods

Question

I try using the parallelStream() in DAO with Spring @Transactional annotations and get so problem:

@Transactional
public void processCollection(Collection<Object> objects) {
    objects.parallelStream()
            .forEach(this::processOne);  //throw exception
}

@Transactional
public void processOne(Object o) {
    ...
}

Works correct:

@Transactional
public void processCollection(Collection<Object> objects) {
    objects.stream()
            .forEach(this::processOne);  //work correctly
}

@Transactional
public void processOne(Object o) {
    ...
}

Exception:

org.hibernate.HibernateException: No Session found for current thread
org.springframework.orm.hibernate4.SpringSessionContext.currentSession(SpringSessionContext.java:106)
org.hibernate.internal.SessionFactoryImpl.getCurrentSession(SessionFactoryImpl.java:978)

How can I use @Transactional annotated methods by parallelStream()?

Update Why this happen Spring transaction manager and multithreading But I hope spring 4 with java 8 support can provide some solution for this. Any ideas?

A trivial question, but do you get the same error if you use stream().parallel()? — Shiraaz.M, Apr 24 '14 at 11:01
http://stackoverflow.com/questions/16835974/spring-transaction-manager-and-multithreading — Evgeni Dimitrov, Apr 24 '14 at 11:15
Thank you Evgeni, I understand why this happen. Work around for this is interesting. — VladS, Apr 24 '14 at 11:34
I am wondering why would you like to have @Transactional on processCollection when you want to run it in parallel. — Ankit Bansal, Apr 24 '14 at 11:50
It's just example, What if it will '@Cacheable' instance of '@Transactional' ? Cache will work for only one thread as I understand.. — VladS, Apr 24 '14 at 12:05

Alexey Malev · Answer 1 · 2014-04-25T13:14:05.263

Well, I have a guess consists of several guesses:

You have session management policy as session-per-thread;
Object you wrote in example is in fact some entity that uses lazy loading;
processOne() method uses entity properties that are loaded lazily;
Because of first point, threads, started for parallelStream() has no session available (probably in ThreadLocal, don't remember how technically sessions are bound to threads);

That altogether causing the problem you have. The behavior looks quite strange to me, so I suggest to do the following:

Remove all lazy loading and try parallelStream() again;
If that succeeds, you'll have to load the entities completely before performing parallelStream().

Alternative way to go: detaching all list elements from session before doing parallelStream().

Although as Marko wrote in comments, Session is not thread-safe, so that means you have to get rid of Session usage either by removing lazy loading, or by detaching all entities from session.

Hibernate's session is not thread-safe. The only option is detachment. — Marko Topolnik, Apr 24 '14 at 12:55

score 6 · Answer 2 · edited Jun 05 '21 at 04:40

The problem is not with parallel stream. In spring transaction is created using AOP.
When your processCollection method is executed spring create a proxy object of this and transaction is started. Calling another method in same class, spring will not run that method in New transaction even if you specified @Transaction . To get it run move that method process() to new service and then execute your problem. Your program will work fine.

Java .parallelStream() with spring annotated methods

2 Answers2

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